Some receivers with built-in antennas, for example those at lower cost, do not have Received Signal Strength Indication (RSSI) circuits built in. Even when present, most such RSSI circuits operate over a very limited range of signal levels and are designed to provide only a slow, crude indication of received signal level to the user. Therefore, unless a receiver has a high quality RSSI circuit built-in, the problem of determining the signal level at the actual receiver's antenna input without affecting the antenna is very difficult involving direct connection through wires in order to provide instrumentation. Even if an excellent RSSI circuit is present that is fast enough, its results again must be sent to outside instrumentation for recording and analysis. In any case, wired connection to things outside the receiver will likely change the antenna pattern and impedance unless aggressive, costly, non-portable, bulky, undesirable, equipment intensive and impractical steps are taken to minimize the impact and there will still be questions about accuracy. The need to make external wired connections seriously limits the trustworthiness and value of results as well as the types of real world situations that could be usefully evaluated.
With present methods and devices that try to measure antenna input signals with a receiver that has a built-in antenna, designers experience significant difficulty in making an accurate measurement of the signal actually received by the in-place antenna and then to track rapid changes. This lack of desired capability has been aggravated by the nature of many existing receivers. For example, commercially produced receivers are often very small and are located within oddly shaped plastic cases that may contain patches of conductive material. The case and its internal printed circuit boards are part of the antenna. Furthermore, many common receivers have limited dynamic range in any given stage because of noise as well as compressive, limiting, or other non-linear gain.
Experimentation was utilized as a prelude to creation of the invention. For example, two methods were attempted to make propagation anomaly and path loss measurements in realistic or rapidly changing situations from a transmitting source. A first method includes replacing an original or initially used antenna and receiver with a surrogate antenna/receiver box and cabling from the antenna/receiver to a remote instrumentation. The problem with this approach is that the antenna pattern likely does not correspond to the original signal; important observable metrics will be changed, including multipath and nearby object effects to the RF field. This method tends to produce repeatable and apparently consistent results, but the results do not accurately represent the true nature of the metrics being studied.
A second experimentation method was attempted entailing attaching a spectrum analyzer at the antenna input or further into the actual receiver. Even with this method, serious difficulties emerged from its use. An active instrumentation probe must be attached to the receiver to prevent loading of the antenna or circuitry. The attachment of an active probe would be difficult inside smaller receiver cases, such as cellphones. Furthermore, the analyzer or recording equipment required would need to be located some distance from the receiver and antenna to avoid an impact on the antenna pattern. This would require increased lengths of cable to connect to the spectrum analyzer, which will become part of the receiver's antenna system. This length of cable would add to the undesirable result of also changing the antenna pattern. Extensive and difficult steps can be taken to mitigate this undesirable effect, but it would be difficult to dispel suspicion that the cables have changed the pattern, or prove that they have not.
A receiver, which is part of a transceiver, could be adapted to incorporate an ability to report back signal level through the transmitter without requiring additional components to be added. These mechanisms can sometimes be quite accurate but have serious drawbacks such being too slow to track rapid changes in received power level due to propagation anomalies, transmitter/receiver motion, or other factors that such an attempted solution would entail.
The present invention relates to a signal measurement system which is adapted to address these and other shortcomings in existing technology. One embodiment of the invention can include a system adapted to remotely measure and rapidly track a signal level at an antenna input of a receiver with built-in antennas in a number of environments (e.g., when that receiver antenna is positioned on a top surface of an automobile, on a seat in a bus and in a subway tunnel are examples of such environments). Such measurement could be used to determine actual device antenna pattern, actual path loss, the impact of propagation anomalies, and other important measurable information in realistic situations well beyond artificial and costly laboratory environments.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrative embodiment exemplifying the best mode of carrying out the invention as presently perceived.